Words and designs are frequently printed onto clothing and other textile materials, and other objects. Common means of applying such designs to objects include the use of silk screens, and mechanically bonded thermal transfers. Silk screen process is well known in the art, and a mechanical thermal process to textile materials is described in Hare, U.S. Pat. No. 4,244,358.
The use of computer technology allows a virtually instantaneous printing of images. For example, video cameras or scanning may be used to capture an image to a computer. The image may then be printed by any suitable printing means, including mechanical thermal printers, wet printed (inkjet) heat sensitive transfers and laser printers. These printers will print in multiple colors.
The process of thermal transfers by mechanical means is described in Hare., U.S. Pat. No. 4,773,953. The resulting mechanical image, as transferred, is a surface bonded image with a raised plastic like feel to the touch. The resulting printed image is stiff to the feel, has poor dimensional stability when stretched and poor color range.
Heat activated transfer ink solids change to a gas at about 400.degree. F., and have a high affinity for polyester at the activation temperature and a limited affinity for most other materials. Once the gassification bonding takes place, the ink is permanently printed and highly resistant to change or fading caused by laundry products.
Images produced by heat activated inks, such as sublimation inks, which are transferred onto textile materials having a cotton component do not yield the high quality image experienced when images formed by such inks are printed onto a polyester substrate. Images which are printed using sublimation inks applied by heat and pressure onto substrates of cotton or cotton and polyester blends yield relatively poor results. The natural tendency of the cotton fiber to absorb the ink causes the image to lose its resolution and become distorted.
To improve the quality of images transferred onto substrates having a cotton component, such substrates are surface coated with materials, such as the polymeric coating described in DeVries et. al., U.S. Pat. No. 4,021,591. Application of the surface coating to the substrate allows the surface coating material to bond the ink layer to the substrate, reducing the absorbency of the ink by the cotton and improving the image quality.
In the prior art, coverage of the surface coating material has not been matched to the image. The surface coating material is applied to the substrate over the general area to which the image layer formed by the inks is to be applied, such as by spraying the material or applying the material with heat and pressure from manufactured transfer sheets, which are usually rectangular in shape. The area coated with the surface coating material is therefore larger than the area covered by the ink layer. The surface coating may be seen extending from the margins of the image. The excess surface coating reduces the aesthetic quality of the printed image on the substrate. Further, the surface coating tends to turn yellow with age, which is undesirable on white and other light colored substrates.
Hale, U.S. Pat. Nos. 5,246,518 and 5,248,363 disclose the use of thermal printers to produce an image on a medium or transfer sheet wherein the image is comprised of sublimation or other heat activated inks. The method described in Hale does not activate the ink during the printing of the medium or transfer sheet.